The present invention relates to a clock recovering device and, more particularly, to a device for accurately recovering a clock from received data which has a different duty ratio of logical ONEs and logical ZEROs.
For the recovery of a clock from received data, it has been customary to detect a transition of the incoming data and, if the recovered clock is low level (or high level) at the instant of detection of a transition, retard (or advance) the phase of the recovered clock deciding that the phase is advanced (or retarded). In this manner, a prior art clock recovering device corrects the phase of a recovered clock timed to transitions of received data. However, a problem with such a device is that when the duty ratio of ONEs and ZEROs of received data is different, even if the phase of a recovered clock is greatly deviated, the phase is decided as being advanced and retarded alternately every time a transition is detected. This indefinitely prevents a clock from being correctly recovered.